How do I install roof mount A/C in MCI MC7 without welding the roof supports?

[oldmansax]

I need advice on installing a third roof mount A/C in my '73 MCI  MC7.

It has three pieces of square tubing running the length of the roof that are not 14" apart. That means I have to cut all three to mount the A/C. Since the bus is already finished I don't want to do any welding in the roof. I am sure someone has done this before.

How is it done?

[Dallas]

Possibly you could weld up your 14" X14" square tube outside the coach and then ad gussets and brackets to it so when you install it you could just bolt it into place.

It wouldn't be nearly as strong as welding it in place, but then I saw one Flx where the cut out the longitudinal member and boxed it in with wood 2X2's. t had been going down the road that way for years with no problem.

I personally wouldn't do that, but it is a thought.

By the way, I still haven't found the box of lightbulbs I told you about. 

[Beatenbo]

I have put roof airs on 3 GMs and 5 MCIs and have never welded anything. I have cut a 14X14 right throuhg that center beam and have never had a problem. I usually cut some strips of 2X2 or 2X4 and sandwich between the roof and ceiling panels. I have 3 ACs on my 102C3 now. However I have always left original ceiling panels and cvered them.That 2X will match right up to that 1 1/2 " beam.

[Ross]

The center channel in the roof is structural.  There may be enough support in the roof skin but I wouldn't just cut out the center channel.  The proper way to do it is to weld in two new 1.5" square tubes parallel and on either side of the original 14" apart.  Once the new ones are in, cut the old one to suit your new AC.  Unfortunately, it can't really be done without some ceiling work.  Depending on how the ceiling is done though, that may not be a big deal.

Ross

[TomC]

I have a transit that is 102" wide and has a relatively flat roof.  I offset all three of my roof A/C's-the front to the right with the middle and rear to the left of the center roof beam.  I just cut out the roof as close to the center beam and to one of the cross beams so that two of the sides were structural ceiling.  The other two sides I just filled in with 1x2" to match the thickness of the rest of the ceiling.  Works well and they don't bounce going down the road.  Good Luck, TomC

[Dreamscape]

On our Eagle we have three roof airs.

They were installed in the middle and the center support was cut. I did not do this, a previous owner did.

During my interior installation I just framed them in with 2x2 wood. They seem to be substantial enough.

When on the roof puting on a Fantastic vent I did not notice any weakness.

I think it has to do with doing it whatever way works for you.

Paul

Dreamscape

[oldmansax]

Thanks for the help & information. I guess I'll just open up the roof & see what it looks like.

[Stan]

The longitudinal framing in the roof of most buses hold up the front and rear of the bus. If you take even a superficial look at a bus you will see that there is nothing holding up the driver portion of the bus except for the roof. The same applies at the rear where the unbalanced  weight of the engine is hanging from the roof.

Cutting the framing without replacing it with a welded in box and cutting holes in the exterior and interior skin will weaken the stucture. It may not fall apart immediately and it may never fall apart but be aware of what you are doing before you do it.

[Buffalo SpaceShip]

I'm with Stan on this one. Either offset the units right or left of center (my 4108 was done that way) or weld back in steel supports/ gussets if you cut the center support and rivet the roof skin to them.

Wood framing is not nearly sufficient to replace the structure removed.

Brian B.

[JimW7]

I have two Penguins on my 7. I offset them mainly for headroom. The instalation manual states they will work fine on the slope of the roof. I forget the exact degree, but it was more than where I put them. They are each 14" off center, one on each side. Where are you going to put it? Front or back? Do you need the max. air flow? Could you stradle one of the frames, reducing air flow slightly, but keeping the roof integrity?
Jim